This invention relates to machines having a reciprocating member that is coupled to a rotatable member and more particularly to the type of machine in which the rotatable member is connected to the reciprocating member in such a way as to produce a stroke that is four times the crankpin offset.
Such machines include one or more reciprocating members that drive a crankshaft through a connecting rod or other connector and/or a crankshaft that drives one or more reciprocating members through a connecting rod and/or other connector. Such machines may transfer kinetic energy back and forth between the crank and the reciprocating member or members. Examples of types of machines that may have a rotatable member connected to the reciprocating member in such a way as to produce a stroke that is four times the crankpin offset are engines, pumps, compressors and mechanisms that convert rotary motion to reciprocating motion and vice versa.
To provide kinetic energy and to minimize vibrations, these mechanisms utilize flywheels and/or a number of reciprocating members to minimize fluctuations in the angular velocity of the crank. In the case of a single piston engine, making the flywheel larger reduces the change in angular velocity of the crank at the top of the stroke when the piston is essentially not moving compared to near midstroke when the piston reaches its maximum speed. Multiple piston engines can space the angle between pistons do not only balance or partially balance the momentums of the pistons but to also minimize changes in the angular momentum of the crank. Both methods require a constant transfer of energy sack and forth from the crankpin to the connecting rod or connector. This results in large forces and friction between the crankpin and the connecting rod or connector at higher RPMs (revolutions per minute).
In those engines and motion converting mechanisms that have a stroke that is four times the crankpin offset and utilize connectors instead of connecting rods, the transfer of energy back and forth between the crankpin and the reciprocating member is even further limiting than just large forces and resulting friction. At the top part of the stroke and at the bottom part of the stroke, the energy is transferred from the crankpin through the connector to the reciprocating member and vice versa. However, this does not occur through a portion of midstroke where there is a second degree of freedom that partially uncouples the primary interface from the crankpin through the connector to the reciprocating member. The energy must be transferred by an intermittent secondary interface.
The secondary interface between the crank and the reciprocating member disclosed in U.S. Pat. No. 4,658,768 issued to Douglas T. Carson on Apr. 21, 1987, for ENGINE and the secondary interface between the connector and the housing as disclosed in U.S. Pat. No. 4,932,373 issued to Douglas T. Carson on Jun. 12, 1990, for MOTION CONVERTING MECHANISM, the disclosures of which are incorporated herein by reference eliminate the second degree of freedom through midstroke.
The forces through this center portion of the stroke are much less than they are in other portions of the stroke, especially if the combustion stroke of an engine where the force from the piston drops off rapidly as the piston moves away from the top of the stroke. Likewise, forces climb rapidly during compression in engines, pumps, and compressors as the piston moves towards the top of the stroke. Because of this, the design of the intermittent secondary interface can generally be much less rugged than that of the primary interface as taught in U.S. Pat. 4,932,373 issued to Douglas T. Carson on Jun. 12, 1990. This is applicable for low and medium RPM machines but would require an ever increasing larger and more rugged secondary interface as the higher RPMs are achieved.
The primary interface which is designed to withstand large forces such as those resulting from combustion and compression can also withstand those forces that occur at the higher RPM machines where the reciprocating member is rapidly slowing down, changing direction, and then speeding up again. This is not typical of the secondary interface, at higher RPMs, as the force necessary to transfer energy back and forth from the crankpin to the reciprocating member approaches the external forces encountered by the primary interface during compression and combustion.
The prior art motion converting mechanism have several disadvantages, such as for example: (1) they restrict the upper limit on RPM and/or demand a larger, more rugged, and more costly secondary interface; (2) the resulting friction encountered by the secondary interface is excessively high; (3) the energy transferred back and forth between the crank and the connector/reciprocating mechanism results in momentary fluctuations in crankshaft RPM where the RPM is higher at the ends of the stroke than through midstroke; and (4) they require additional moving components, as described in U.S. Pat. Nos. 4,658,768 and 4,932,373 (see above), other than the basic unit consisting of one crank assembly, one connector and one reciprocating member to fully balance the machine.